The present invention relates to a fuel injection control system for a two-cycle engine having an electronic control system such as a microcomputer.
The electronic control system having the microcomputer is commonly and widely used for controlling various components of the engine. In the system, quantity of fuel injection is calculated by the microcomputer based on the engine operating condition parameters detected by various sensors. A drive signal in dependency on fuel injection pulse width corresponding to the fuel injection quantity is applied to a fuel injector to inject fuel from the injector at a predetermined timing.
The fuel injection control system having the microcomputer is used in a four-cycle engine.
A recent two-cycle engine is also equipped with an electronic fuel injection control system. Japanese Patent Application Laid-Open 63-255543 discloses such an electronic fuel injection control system for the engine. The system has a main intake pipe for inducing fresh air to a crankcase and a sub intake pipe for directly inducing fresh air to the crankcase. A fuel injector is provided in each of the intake pipes. An electronic control unit is provided for controlling the injection timing and quantity of fuel injected from the fuel injector. In general, fuel injection timing is controlled in synchronism with engine speed.
In the four-cycle engine, the combustion in the engine is performed once at every 720 degrees of crank angle, that is two rotations of the engine. In order to supply a necessary amount of fuel to the cylinder, there are various methods such as all-cylinder simultaneous injection, group injection and sequential injection.
In the all-cylinder simultaneous injection method, one-half of necessary amount of fuel for all cylinders is injected at the same time per one rotation of the engine. In the group injection method, necessary amount of fuel is injected for every groups of the cylinders per two rotations of the engine. In the sequential injection method, necessary amount of fuel is injected for each cylinder per two rotations of the engine.
On the other hand, in the two-cycle engine, combustion is performed at every 360 degrees of crank angle, that is per one rotation of the engine. Thus, necessary amount of fuel is supplied at every one rotation of the engine.
The combustion stroke of the two-cycle engine is twice as many as the four-cycle engine when the two-cycle engine runs at the same speed as the four-cycle engine. Thus, a high power is produced by the two-cycle engine. To the contrary, a larger amount of fuel is consumed in the two-cycle engine, so that it is necessary to provide a fuel injector having a large capacity. Furthermore, the amount of fuel in a high engine speed range and in a heavy engine load range is largely different from that in a low engine speed range and in a light engine load range. If the capacity of the fuel injector is small, the fuel injection pulse width, that is opening period of the fuel injector must be largely increased in the high engine speed range and in the heavy engine load range. Since the combustion stroke is performed at every 360 degrees, the injector does not have a time to reset. As a result, the injector is kept open to cause not only malfunction of the control system but also of fuel.
However, if the capacity of the injector is increased, the fuel injection pulse width must be largely reduced in a low engine speed range and in a light engine load range. Consequently, the opening period of the injector becomes very short which may shorter than a functional limit of the injector. Therefore, the amount of the injected fuel fluctuates, thereby varying the engine speed and causing the engine stall.